A large part of gold's allure is its rarity. Even so, it's still 1000 times more abundant on Earth than it should be. Boffins at University of Bristol now have an explanation for this phenomenon: it came from ouuuuter spaaaaaace!

In theory, most of the gold, and other heavier metals like tungsten, that were around during Earth's inception would have been sucked into the core during its formation because of their relatively high mass and density; thus leaving behind a crust bereft of bling. While this makes sense logically, it clearly doesn't mesh with reality. Humans have been mining gold for millennia despite not having access to the core.

After comparing tungsten concentrations from samplings of the world's oldest rocks (formed about 4 billion years ago) with those of more modern rocks, scientists found that modern rocks contain significantly more tungsten than their ancient counterparts. Since gold, tungsten, and precious metals in general behave similarly when it comes to geological formation, this means that the original crust contained far fewer precious metals than modern ones. Through further research, they were able to link this change to an exact event: the "terminal bombardment".

Far from being an Schwarzenneger movie, "terminal bombardment" refers to a gigantic meteor shower (or rather hurricane) that took place around 3.9 billion years ago. It consisted of 20 billion billion tons [not a typo] of meteorites crashing into the recently-formed Earth's crust. Damn, nature... It's these asteroids that endowed Earth with virtually all the metals that we've come to depend on for so many purposes. After all, where would civilization be today without grillz? [University of Bristol, BBC] Image from NASA: William Moede et al